Optical element, optical system using optical element, and optical device with optical element

ABSTRACT

In an optical element (B 1 ) prepared by integrally forming, on surfaces of a transparent member, a refracting surface (R 2 ) for receiving a light beam, a plurality of reflecting surfaces (R 3,  R 4,  R 5 ) with curvatures, and a refracting surface (R 6 ) for outputting the light beam reflected by the plurality of reflecting surfaces, a reference portion ( 7 ) for defining the position of the optical element in a predetermined direction with respect to a Y′-Z′ plane including an incident reference axis ( 5 ) and an exit reference axis ( 5 ) of at least one reflecting surface of the optical element (B 1 ) is formed on the optical element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical element and an opticalsystem using the same and, more particularly, to an optical systemelement suitable for, e.g., a video camera, still video camera, copyingmachine, and the like, and an optical system using the same.

The present invention also relates to an optical device which is usedin, e.g., a silver halide camera, video camera, electronic still camera,or the like, and comprises an optical element formed integrally with aplurality of refracting surfaces and a plurality of reflecting surfaces.

2. Description of Related Art

Conventionally, as a photographing optical system, some components ofwhich are built by reflecting surfaces, a so-called mirror opticalsystem (reflection optical system), as shown in FIG. 12, is known.

FIG. 12 is schematic view showing principal part of a mirror opticalsystem made up of one concave mirror and one convex mirror. In themirror optical system shown in FIG. 12, an object light beam 104 comingfrom an object is reflected by a concave mirror 101, and propagates as aconverging beam toward the object side. The light beam is reflected by aconvex mirror 102, and thereafter, is refracted by a lens 110, thusforming an image on an image surface 103.

This mirror optical system is based on an arrangement of a so-calledCassegrainian reflecting telescope, and aims at shortening the totallength of the optical system by folding the optical path of a telescopelens system with a large total lens length made up of a refraction lensusing two reflecting mirrors.

In an objective lens system, such a telescope system, a large number ofmethods for shortening the total lengths of optical systems using aplurality of reflecting mirrors are known in addition to theCassegrainian type for the same purpose as above.

In this manner, a compact mirror optical system is conventionallyobtained by efficiently folding the optical path using a reflectingmirror in place of a lens of a photographing lens with a large totallens length.

However, in general, mirror optical systems such as a Cassegrainianreflecting telescope and the like suffer a problem that some objectlight rays are eclipsed by the convex mirror 102. This problem is causedby the presence of the convex mirror 102 in the passage region of theobject light beam 104.

In order to solve this problem, there has also been proposed a mirroroptical system that uses a decentered reflecting mirror to avoid thepassage region of the object light beam 104 from being shielded by otherportions of the optical system, i.e., to separate main rays of the lightbeam from an optical axis 105.

FIG. 13 is a schematic view showing principal part of a mirror opticalsystem disclosed in U.S. Pat. No. 3,674,334. This optical solves theproblem of eclipse using portions of reflecting mirrors which arerotationally symmetrical about the optical axis.

The mirror optical system shown in FIG. 13 includes a concave mirror111, a convex mirror 113, and a concave mirror 112 in the passage orderof a light beam, and these mirrors are originally rotationallysymmetrical about an optical axis 114, as indicated by two-dashed chainlines in FIG. 13. Of these mirrors, only the upper side of the concavemirror 111, the lower side of the convex mirror 113, and the lower sideof the concave mirror 112 with respect to the optical axis 114 on theplane of the drawing are used, thus constituting an optical system thatseparates main rays 116 of an object light beam 115 from the opticalaxis 114 and avoids the object light beam 115 from being eclipsed.

FIG. 14 is a schematic view showing principal part of a mirror opticalsystem disclosed in U.S. Pat. No. 5,063,586. The mirror optical systemshown in FIG. 14 solves the above problem by decentering the centralaxis itself of each reflecting mirror. In FIG. 14, if an axisperpendicular to an object surface 121 is defined to be an optical axis127, central coordinates and central axes (an axis that connects thecenter of the reflecting surface and the center of curvature of thatsurface) 122 a, 123 a, 124 a, and 125 a of a convex mirror 122, aconcave mirror 123, a convex mirror 124, and a concave mirror 125 in thepassage order of a light beam are decentered from the optical axis 127.In this mirror optical system, by appropriately setting the decenteringamounts and the radii of curvature of the individual surfaces at thattime, an object light beam 128 can be prevented from being eclipsed bythese reflecting mirrors, and an object image is efficiently formed onan imaging surface 126.

Also, U.S. Pat. Nos. 4,737,021 and 4,265,510 disclose an arrangement foravoiding eclipse using portions of reflecting mirrors which arerotationally symmetrical about the optical axis, and an arrangement foravoiding eclipse by decentering the central axis itself of eachreflecting mirror from the optical axis.

As described above, by decentering the reflecting mirrors that build themirror optical system, an object light beam can be avoided from beingeclipsed. However, since the individual reflecting mirrors must be setto have different decentering amounts, a structure that attaches thesereflecting mirrors is complicated, and it becomes very difficult toassure high alingnment precision.

As one method of solving this problem, for example, a mirror system maybe formed as a block to avoid assembly errors of optical parts uponassembly.

As conventional blocks having a large number of reflecting surfaces, forexample, optical prisms such as a pentagonal roof prism, a Porro prism,and the like, which are used in a finder system or the like, a colorseparation prism that separates a light beam coming from a photographinglens into three, i.e., red, green, and blue color light beams and formsobject images based on the individual color light beams on the surfacesof corresponding image sensing elements, and the like are known.

In these prisms, since a plurality of reflecting surfaces are integrallyformed, the relative positional relationship among the reflectingsurfaces is accurately determined, and the positions of the reflectingsurfaces need not be adjusted.

However, the principal function of such prisms is to reverse an image bychanging the traveling directions of light rays, and each reflectingsurface is defined by a plane.

In contrast to this, an optical system in which reflecting surfaces of aprism have curvatures is also known.

FIG. 15 is a schematic view showing principal part of an observationoptical system disclosed in U.S. Pat. No. 4,775,217. This observationoptical system allows an observer to observe the landscape of the outerfield and also to observe an image displayed on an information displaymember overlapping the landscape.

In this observation optical system, a display light beam 145 originatingfrom an image displayed on an information display member 141 isreflected by a surface 142, and propagates toward the object side. Thelight beam is then incident on a half mirror surface 143 defined by aconcave surface. The light beam is reflected by the half mirror surface143, and becomes a nearly collimated light beam by the refractive powerof the concave surface 143. After the light beam is refracted by andtransmitted through a surface 142, it forms an enlarged virtual image ofthe displayed image and enters the pupil 144 of the observer, thusmaking the observer to see the displayed image.

On the other hand, an object light beam 146 from an object is incidenton and refracted by a surface 147 which is nearly parallel to thereflecting surface 142, and reaches the half mirror surface 143 as theconcave surface. Since a semi-transparent film is deposited on theconcave surface 143, some light components of the object light beam 146are transmitted through the concave surface 142, are refracted by andtransmitted through the surface 142, and then enter the pupil 144 of theobserver. With these light components, the observer visually observesthe displayed image overlapping the landscape of the outer field.

FIG. 16 is a schematic view showing principal part of an observationoptical system disclosed in Japanese Patent Laid-Open Patent No.2-297516. This observation optical system also allows the observer toobserve the landscape of an outer field, and to observe an imagedisplayed on an information display member overlapping the landscape.

In this observation optical system, a display light beam 154 originatingfrom an information display member 150 is transmitted through a flatsurface 157, that builds a prism Pa, to enter the prism Pa, and thenstrikes a parabolic reflecting surface 151. The display light beam 154is reflected by the reflecting surface 151 to be converted into aconverging light beam, and forms an image on a focal plane 156. At thistime, the display light beam 154 reflected by the reflecting surface 151reaches the focal plane 156 while being totally reflected by twoparallel flat surfaces 157 and 158 that build the prism Pa, thusachieving a low-profile optical system as a whole.

The display light beam 154 that leaves the focal plane 156 as adiverging light beam is incident on a half mirror 152 defined by aparabolic surface while being totally reflected between the flatsurfaces 157 and 158, and is reflected by the half mirror surface 152.At the same time, the light beam 154 forms an enlarged virtual image ofthe displayed image by the refractive power of the half mirror surface152, and becomes a nearly collimated light beam. The light beam istransmitted through the surface 157 and enters a pupil 153 of theobserver, thus making the observer to recognize the displayed image.

On the other hand, an object light beam 155 coming from an outer fieldis transmitted through a surface 158 b that builds a prism Pb, istransmitted through the half mirror 152 defined by the parabolicsurface, and is transmitted through the surface 157 to enter the pupil153 of the observer. The observer visually observes the displayed imagethat overlaps the landscape of the outer field.

In this reference as well, the displayed image is observed and an objectimage can also be recognized by the arrangement similar to that in U.S.Pat. No. 4,775,217.

Furthermore, Japanese Patent Application Nos. 7-65109 and 7-123256disclose a zoom optical system which has a plurality of transparentoptical elements, each of which is formed integrally with a plurality ofrefracting surfaces and a plurality of reflecting surfaces, so that alight beam enters the transparent optical element from one refractingsurface, and leaves externally from another refracting surface after itis repetitively reflected by the plurality of reflecting surfaces. Also,an image sensing device which forms an image on a solid-state imagesensing element using such an optical system is disclosed in JapanesePatent Application Nos. 7-65104, 7-65106, 7-65107, 7-65108, and 7-65111.

SUMMARY OF THE INVENTION

As a conventional optical prism with reflecting surfaces havingcurvatures normally suffers larger variations in optical performance dueto decentering errors of the reflecting surfaces than an optical prismmade up of only flat surfaces, the allowable positional precision ofeach reflecting surface is very strict, and such optical prism is noteasy to manufacture.

When such optical prism is moved for focusing or zooming, the opticalprism and a holding member for holding it must be precisely coupled toeach other. However, in U.S. Pat. No. 4,775,217, Japanese PatentLaid-Open No. 2-297516, and the like disclose the arrangements of suchoptical prisms alone, but do not mention any methods of guaranteeing thepositional precision of the reflecting surfaces and the optical prismitself, any holding method of the holding member, and the like.

In a conventional coaxial optical system, the optical system can beinspected with reference to its optical axis in the manufacture,measurements, assembly, and the like. However, in such optical prismwhich has decentered reflecting surfaces without any optical axis, amethod of setting a reference portion that serves as a reference uponinspecting the optical system in the manufacture, measurements,assembly, and the like of such optical system is indispensable.

It is an object of the present invention to provide an optical elementand an optical system using the same, which can improve precision in themanufacture, assembly, and measurements of an optical element, and canprevent optical performance from deteriorating.

Also, the present invention has the following objects:

i) to make a reference portion in the optical element easy to use bylimiting a specific direction to a parallel direction and/or aperpendicular direction;

ii) to accurately and securely hold the optical element on a holdingmember or the like by forming an auxiliary portion for assistingposition determination of the optical element in addition to thereference portion to be parallel or perpendicular to the referenceportion, and arranging at least one auxiliary portion to oppose thereference portion;

iii) to satisfactorily hold the holding member and the optical elementupon holding the optical element by setting the reference and auxiliaryportions so that the position of the center of gravity of a regionsandwiched between the reference and auxiliary portions substantiallymatches that of the optical element;

iv) to obtain an optical element which suffers less ghost, can preventthe reference portion and/or the auxiliary portion from shieldingeffective light rays, and can reduce harmful light rays that may beproduced by the reference portion and/or the auxiliary portion, byforming the reference portion and/or the auxiliary portion on a regionother than the light ray effective portion of the optical element;

v) to satisfactorily hold and fix an optical element in correspondencewith every situations by defining the reference portion and/or theauxiliary portion by a plurality of flat surfaces, hole portions, orprojections;

vi) to arrange a holding member that holds the optical element to moveor fix the optical element, and to precisely position the holding memberand the optical element by forming, on the holding member, portions thatfit or join the reference portion and/or the auxiliary portion formed onthe optical member;

vii) to obtain an optical element suffering less ghost, which caneliminate harmful light rays entering the optical element from theholding member as much as possible by forming a predetermined air gapbetween the holding member and the optical element in a region otherthan the fitting or joining portions when the optical element and theholding member for the optical element are fitted or joined to eachother;

viii) to obtain a high degree of parallelism between the central axis ofa fitting hole and a plane including a reference axis by integrallyforming the fitting hole for receiving a guide bar for moving theoptical element in the optical element;

ix) to set the central axis of the fitting hole to be parallel to theincident reference axis of the optical element by forming the fittinghole for receiving the guide bar for moving the optical element in theoptical element, and to eliminate changes in posture upon movement ofthe optical element as much as possible when an optical system is builtusing the optical element; and

x) to further eliminate changes in posture upon movement of the opticalelement when an optical system is built using the optical element, bysetting the central axis of the fitting hole to be parallel to theincident reference axis of the optical element in a plane including thereference axis of the optical element.

On the other hand, none of the above-mentioned prior arts touch upon anymethod of attaching an optical element.

The present invention has been made in consideration of such situation,and has as its object to prevent deterioration of optical performancedue to the way of attaching an optical element in an optical devicewhich comprises an optical element which is arranged so that a lightbeam enters the optical element from one refracting surface, and leavesexternally from another refracting surface after it is repetitivelyreflected by a plurality of reflecting surfaces.

None of the above-mentioned prior arts mention any structure of anoptical device that takes changes in temperature into consideration.

The present invention has been made in consideration of such situation,and has as its object to prevent an image from deteriorating due toexpansion and shrinkage of an optical element due to changes intemperature, changes in refractive index due to such expansion orshrinkage, and the like, in an optical device comprising a zoom opticalsystem having a plurality of optical elements each of which is arrangedso that a light beam enters the optical element from one refractingsurface, and leaves externally from another refracting surface after itis repetitively reflected by a plurality of reflecting surfaces, and adriving means for zoom-driving the zoom optical system.

Furthermore, Japanese Patent Application Nos. 7-65109 and 7-123256 donot mention size reduction of such optical device. On the other hand,Japanese Patent Application Nos. 7-65104, 7-65106, 7-65107, 7-65108, and7-65111 propose a low-profile structure of such optical device, butapply it to a driving source different from a general driving motor.

The present invention has been made in consideration of such situation,and has as its object to attain a size reduction of an optical devicecomprising a zoom optical system having a plurality of optical elementseach of which is arranged so that light beam enters the optical elementfrom one refracting surface, and leaves externally from anotherrefracting surface after it is repetitively reflected by a plurality ofreflecting surfaces, and a driving means for zoom-driving the zoomoptical system.

None of the above-mentioned prior arts mention in detail a structure fordriving an optical element with high precision.

The present invention has been made in consideration of such situation,and has as its object to realize high-precision zoom driving in anoptical device comprising a zoom optical system having a plurality ofoptical elements each of which is arranged so that light beam enters theoptical element from one refracting surface, and leaves externally fromanother refracting surface after it is repetitively reflected by aplurality of reflecting surfaces, and a driving means for zoom-drivingthe zoom optical system.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an optical system according to anembodiment of the present invention;

FIG. 2 is a perspective view of an optical element according to thefirst embodiment of the present invention;

FIG. 3 is an explanatory view showing a case wherein the optical elementof the first embodiment is held by a holding member;

FIG. 4 is a front view showing a case wherein an optical element isimproperly coupled to a holding member to form an optical system;

FIG. 5 is a front view showing a case wherein the optical element of thefirst embodiment is coupled to the holding member to form an opticalsystem;

FIG. 6 is a perspective view of an optical element according to thesecond embodiment of the present invention;

FIG. 7 is a perspective view of an optical element according to thethird embodiment of the present invention;

FIG. 8 is a perspective view of an optical element according to thefourth embodiment of the present invention, and an optical system usingthe same;

FIG. 9 is a perspective view of an optical element according to thefifth embodiment of the present invention;

FIG. 10 is a perspective view of an optical element according to thesixth embodiment of the present invention;

FIG. 11 is an explanatory view of a coordinate system that definesconfiguration data of the optical system of the present invention;

FIG. 12 is a schematic view showing principal part of a conventionalreflecting optical system;

FIG. 13 is a schematic view showing principal part of a conventionalreflecting optical system;

FIG. 14 is a schematic view showing principal part of a conventionalreflecting optical system;

FIG. 15 is a schematic view showing principal part of a conventionalobservation optical system;

FIG. 16 is a schematic view showing principal part of a conventionalobservation optical system;

FIG. 17 is a perspective view of an image sensing device according tothe seventh embodiment of the present invention;

FIG. 18 is a plan view of FIG. 17;

FIG. 19 is a side view of FIG. 17;

FIG. 20 is a perspective view of the image sensing device excludingfirst, second, and third optical elements;

FIG. 21 is a view for explaining the optical axes of incident light andreflected light;

FIG. 22 is a view showing the optical paths of incident light andreflected light;

FIG. 23 is a perspective view of an image sensing device according tothe eighth embodiment of the present invention;

FIG. 24 is a side view of FIG. 23; and

FIG. 25 is a view showing the shape of an optical element according tothe ninth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An optical element of the present invention and an optical system usingthe same do not have any symmetrical axis like an optical axis in anormal optical system. Hence, in the optical system of the presentinvention, a “reference axis” corresponding to the optical axis in thecoaxial system is set, and the arrangement of individual elements in theoptical system will be described on the basis of the reference axis.

Definition of the reference axis will be given below. In general, theoptical path of a certain light ray of a reference wavelength thatleaves an object surface and reaches an image surface, and serves as areference is defined as the “reference axis” in that optical system.However, since this definition alone cannot define a light ray thatserves as a reference, the reference axis light ray is normally setaccording to one of the two following rules:

Rule 1: When an axis in which an optical system has symmetry, albeitpartially is present, and an aberration correction can be symmetricallymade about this axis, a light ray that propagates along the symmetryaxis is defined as the reference axis light ray.

Rule 2: When no symmetry axis is generally present in an optical system,or when an aberration correction cannot be symmetrically made about asymmetrical axis even if such symmetrical axis is partially present, alight ray that leaves the center of the object surface (the center ofthe range to be photographed or observed), passes through an opticalsystem in the order of designated surfaces of the optical system, andpasses through the center of a stop in the optical system, or a lightray that passes through the center of the stop in the optical system andreaches the center of the final image surface, is set as the referenceaxis light ray, and its optical path is defined to be the referenceaxis.

The reference axis defined in this manner normally has a folded shape.In each surface, the intersection between the surface and the referenceaxis light ray is defined to be a reference point, the reference axislight ray on the object side of each surface is defined as an incidentreference axis, and the reference axis light ray on the image side ofeach surface is defined as an exit reference axis. Furthermore, thereference axis has a direction, which is assumed to be a direction inwhich the reference axis light ray propagates upon forming an image.Hence, an incident reference axis direction and an exit reference axisdirection are respectively present on the incident and exit sides. Inthis manner, the reference axis finally reaches the image surface whilechanging its direction in accordance with the refraction or reflectionrule in the order of surfaces which is set in advance. In an opticalelement (optical system) made up of a plurality of surfaces, thereference axis light ray that enters a surface closest to the objectside is defined to be an incident reference axis of that optical element(optical system), and the reference axis light ray that leaves from asurface closest to the image side is defined to be an exit referenceaxis of that optical element (optical system). The definitions of thedirections of these incident and exit reference axes are the same asthose of the surfaces.

Prior to a description of the embodiments, the method of expressingconfiguration data of the embodiments, and common factors throughout theembodiments will be explained below.

FIG. 11 is an explanatory view of a coordinate system that definesconfiguration data of the optical system of the present invention. In anembodiment of the invention, a surface at an i-th position along onelight ray (indicated by a dotted line in FIG. 11 and to be referred toas a reference axis light ray hereinafter) that travels from the objectside toward the image side will be referred to as an i-th surfacehereinafter.

In FIG. 11, a first surface R1 is a stop (an aperture), a second surfaceR2 is a refracting surface coaxial with the first surface, a thirdsurface R3 is a reflecting surface which is tilted with respect to thesecond surface R2, fourth and fifth surfaces R4 and R5 are reflectingsurfaces which are respectively shifted and tilted with respect to theirprevious surfaces, and a sixth surface R6 is a refracting surface whichis shifted and tilted with respect to the fifth surface R5. The secondto sixth surfaces R2 to R6 are formed on a single optical element madefrom a medium such as glass, plastic, or the like, and this opticalelement is referred to as an optical element B1 in FIG. 11.

Hence, in the arrangement in FIG. 11, the medium from an object surface(not shown) to the second surface R2 is air, the media between adjacentones of the second to sixth surfaces R2 to R6 are a certain commonmedium, and the media between the sixth surface R6 and a seventh surfaceR7 (not shown) is air.

Since the optical system of the present invention is a decenteredoptical system, the individual surfaces that build the optical system donot have any common optical axis. In this embodiment, an “absolutecoordinate system of the optical system” having, as an origin, thecenter of the light ray effective diameter of the first surface servingas the stop is set. In the present invention, the individual axes of theabsolute coordinate system of the optical system are set as follows.

Z-axis: the reference axis that passes through the origin and extendstoward the second surface R2

Y-axis: a straight line that passes through the origin and 90°counterclockwise with the Z-axis within a tilt plane (within the planeof the drawing of FIG. 11)

X-axis: a straight line that passes through the origin and isperpendicular to the Z- and Y-axes (a straight line perpendicular to theplane of the drawing of FIG. 11)

Since the surface shape of the i-th surface that builds the opticalsystem is preferably expressed by setting a local coordinate systemwhich has, as a reference point, the intersection between the referenceaxis and the i-th surface so as to allow easier understanding than thatexpressed by the absolute coordinate system upon recognizing the shape,numerical value data of each embodiment of the present invention expressthe surface shape of the i-th surface by the local coordinate system.

The tilt angle of the i-th surface in the Y-Z plane is expressed by anangle θi (unit: °) which has a positive value in the counterclockwisedirection with respect to the Z-axis of the absolute coordinate systemof the optical system. Hence, in this embodiment, the origin of thelocal coordinate system of each surface is present on the Y-Z plane inFIG. 11. Neither tilt nor shift take place in the X-Z and X-Y planes.Furthermore, the y- and z-axes of the local coordinate system (x, y, z)of the i-th surface are tilted by the angle θi in the Y-Z plane withrespect to the absolute coordinate system (X, Y, Z) of the opticalsystem, and are set as follows:

z-axis: a straight line that passes through the origin of the localcoordinate system, and makes the angle θi counterclockwise in the Y-Zplane with the Z-direction of the absolute coordinate system of theoptical system

y-axis: a straight line that passes through the origin of the localcoordinate system and 90° counterclockwise in the Y-Z plane with thez-direction

x-axis: a straight line that passes through the origin of the localcoordinate system, and is perpendicular to the Y-Z plane

Also, Di is the scalar quantity that represents the interval between theorigins of the local coordinate systems of the i-th and (i+1)-thsurfaces, and Ndi and νdi are respectively the refractive index andAbbe's number of the medium between the i-th and (i+1)-th surfaces. Notethat the stop and the final imaging surface are displayed as independentflat surfaces.

Each embodiment of the present invention has a spherical surface and anaspherical surface with rotational asymmetry. Of these surfaces, aspherical surface portion is assumed to have a spherical shape and isdescribed with its radius Ri of curvature. Assume that the radius Ri ofcurvature has a positive sign when the center of curvature points in theplus direction of the z-axis of the local coordinate system, and has aminus sign when the center points in the minus direction of the z-axis.

The spherical surface has a shape expressed by the following equation(1): $\begin{matrix}{z = \frac{\left( {x^{2} + y^{2}} \right)/R_{i}}{1 + \left\{ {1 - {\left( {x^{2} + y^{2}} \right)/R_{i}^{2}}} \right\}^{1/2}}} & (1)\end{matrix}$

The optical system of the present invention has at least onerotation-asymmetric aspherical surface, whose shape is expressed by thefollowing equation (2): $\begin{matrix}{z = {{A/B} + {C_{02}y^{2}} + {C_{11}x\quad y} + {C_{20}x^{2}} + {C_{03}y^{3}} + {C_{12}x\quad y^{3}} + {C_{21}x^{2}y} + {C_{30}x^{3}} + {C_{04}y^{4}} + {C_{13}x\quad y^{3}} + {C_{22}x^{2}y^{2}} + {C_{31}x^{3}y} + {C_{40}x^{4}} + {\bullet\bullet\bullet\bullet\bullet}}} & (2)\end{matrix}$

for

A=(a+b)·(y ²·cos² t+x ²)B = 2a  •b  •cos  t[1 + {(b − a)•y • sin  t/(2a  •b)}+  ([1 + {(b − a)•y • sin  t/(a  •b)} − {y²/(a  •b)} − {4a  •b • cos²t   +   (a + b)²sin²t}x²/(4a²²cos²t)])^(1/2)]

Note that the shape of each rotation-asymmetrical surface in the presentinvention is set to have a shape symmetrical about the y-z plane byusing only even-numbered order terms associated with x and settingodd-numbered order terms at “0” in the above equation that representsthe curved surface.

When the condition given by equation (3) below is satisfied, the surfacehas a shape symmetrical about the x-z plane:

C₀₃=C₂₁=t=0  (3)

Furthermore, when the condition given by equation (4) below issatisfied, that surface has a shape with rotation symmetry:

C ₀₂ =C ₂₀ =C ₀₄ =C ₄₀ =C ₂₂/2  (4)

If neither conditions are satisfied, the surface has a shape withrotation asymmetry.

In the numerical value data, a horizontal half field angle uY is themaximum field angle of a light beam which is incident on the firstsurface R1 in the Y-Z plane in FIG. 11, and a vertical half field angleuX is the maximum field angle of a light beam which is incident on thefirst surface R1 in the X-Z plane.

As data that represents the brightness of the optical system, thediameter of a stop (aperture)(entrance pupil) represents the stop(aperture) diameter. Also, an image size is the effective image range onthe image surface. The image size is expressed by a rectangular regiondefined by “horizontal” indicating the size in the y-direction and“vertical” indicating the size in the x-direction both of the localcoordinate system.

FIG. 1 is a sectional view of an optical system according to oneembodiment of the present invention, and shows an optical path.Reference numeral B1 denotes an optical element formed integrally with aplurality of reflecting surfaces with curvatures. The optical element B1is prepared by forming on the surfaces of a transparent member, anincident refracting surface R2, five reflecting surfaces, i.e., aconcave mirror R3, a convex mirror R4, a concave mirror R5, a convexmirror R6, and a concave mirror R7, and an exit refracting surface R8along the reference axis light ray in the order from the object side.These refracting surfaces and reflecting surfaces are symmetrical aboutthe plane of the drawing (Y-Z plane), and hence, all the reference axesare included in the Y-Z plane. The direction of the incident and exitreference axes of the optical element B1 are antiparallel to each other.Note that a reflecting film is formed on each reflecting surface.Furthermore, the optical element B1 has two side surfaces parallel tothe plane of the drawing.

Reference numeral 2 denotes an optical correction plate such as a quartzlow-pass filter, an infrared cut filter, or the like; and 3, a finalimaging surface, where the image sensing surface of an image sensingelement such as a CCD or the like is located. Reference numeral 4denotes a stop arranged on the object side of the optical element B1;and 5, a reference axis of the optical system.

The imaging process in this embodiment will be explained below. Theamount of an incident light beam 6 coming from an object is limited bythe stop 4, and the light beam 6 is incident on the incident refractingsurface R2 of the optical element B1. The light beam 6 is refracted bythe surface R2, and reaches the concave mirror R3.

The concave mirror R3 reflects the object light beam 6 toward the convexmirror R4, and forms a primary object image on an intermediate imagingsurface N1 by the power of the concave mirror.

In this manner, since the object image is formed in the optical elementB1 in an early stage, an increase in light ray effective diameter of thesurfaces arranged on the image side due to the stop 4 is suppressed.

The object light beam 6 that formed the primary image on theintermediate imaging surface N1 is reflected in turn by the convexmirror R4, concave mirror R5, convex mirror R6, and concave mirror R7,and reaches the exit refracting surface R8 while being influenced by thepowers of these reflecting mirrors. The light beam 6 is refracted by thesurface R8, and leaves the optical element B1. The object light beam 6is then transmitted through the optical correction plate 2, and forms animage on the final image surface 3.

In this manner, the optical element B1 serves as a lens unit which hasdesired optical performance while repeating reflections by the pluralityof reflecting mirrors with curvatures, has an imaging effect as a whole,and has a very low profile in the X-direction.

In this optical system, focusing is attained by moving the opticalelement B1 in a direction parallel to its incident reference axis.

FIG. 1 shows an example of the optical system of the present invention.As another optical system of the present invention, a zooming opticalsystem which has a plurality of optical elements each of which isintegrally formed with a plurality of reflecting surfaces withcurvatures, and moves these optical elements to attain zooming is alsoavailable.

Since the optical system of the present invention is used while beingbuilt in a video camera, still video camera, copying machine, or thelike, the image sensing element, the optical correction plate, and thelike are fixed to the main body (not shown), and the optical element B1of this embodiment is coupled to a holding member and is attached to bemovable with respect to the main body, thus building the optical system.

The XYZ coordinate system shown in FIG. 1 is the absolute coordinatesystem of the optical system, and is assumed to be set on the main body.

[First Embodiment]

FIG. 2 is a perspective view of an optical element according to thefirst embodiment of the present invention. The same reference numeralsin FIG. 2 denote the same parts as in FIG. 1. Note that an X′Y′Z′coordinate system shown in FIG. 2 is an “absolute coordinate system ofan optical element”, and the individual axes are set as follows to have,as the origin, a reference point (a reference point of an incidentrefracting surface R2 in this embodiment) of a certain surface presenton a plane (its definition will be described later) including thereference axis of the optical element:

Z′-axis: the incident reference axis to the reference point

Y′-axis: a straight line that passes through the origin in the planeincluding the reference axis of the optical element, and 90°counterclockwise with the Z-axis

X′-axis: a straight line that passes through the origin and isperpendicular to the Z′- and Y′-axes.

In all the optical elements of the individual embodiments to bedescribed below, the X′Y′Z′ coordinate system is the one describedabove.

In FIG. 2, reference numeral 7 denotes a reference portion, which isformed by three surfaces 7 a, 7 b, and 7 c, and another surface on aside surface (to be referred to as a forming surface in the sense offorming the reference portion) of an optical element B1, and defines theposition of the optical element B1 in a specific direction.

Of the surfaces that form the reference portion 7, the surface 7 a isparallel to a plane (Y′-Z′ plane) including a reference axis 5, anddefines the position of the optical element B1 on the Y′-Z′ plane. Onthe other hand, the surfaces 7 b and 7 c are perpendicular to the plane(Y′-Z′ plane) including the reference axis 5. The surface 7 b definesthe position of the optical element B1 on the Z′-X′ plane, and thesurface 7 c defines the position of the optical element B1 on the X′-Y′plane.

The reference portion 7 defines the position of the optical element B1in a specific direction with respect to a plane that includes anincident and exit reference axes of at least one reflecting surface ofthe optical element B1.

In this manner, since the position of the optical element B1 is definedusing the reference portion 7, the relative positional relationshipamong the individual surfaces that define the optical element B1 and thereference portion 7 can be expressed to allow easy understanding.

In a conventional coaxial optical system, a single axis common to lensesthat build that optical system is present as its name implies, and thecharacteristics of the individual lenses can be two-dimensionallyexpressed with reference to this axis.

However, in an optical element that allows a free three-dimensionallayout of the individual surfaces as in this embodiment, an axis thatserves as a reference in design may be set, but it is hard to set anaxis that serves as a reference from its outer appearance.

For this reason, in this embodiment, a reference portion is set on theoptical element, so that a coordinate system normally set on a virtualspace can be set on the optical element in a visible form. With thiscoordinate system, when the optical element of this embodiment is formedby molding, the individual surfaces can be worked with reference to thereference portion 7 upon working molds used in formation by molding.Also, when the positional relationship among the individual surfaces ofa molded product is measured with reference to the reference portion 7,the mold working data and the measurement data of the molded product canbe made common. Even when errors have occurred during working, theworking data can be easily corrected based on the measurement data, andthe optical element can be worked with high precision.

In this embodiment, an auxiliary portion 8 is formed on the opticalelement B1 in addition to the reference portion 7 to improve the holdingprecision of the optical element. The reference portion 7 is formed onone side surface of the optical element, and the auxiliary portion 8 isformed at a position facing the reference portion 7 on another sidesurface (forming surface) to have a shape similar to that of thereference portion 7. That is, the auxiliary portion 7 has surfaces,which respectively correspond to the surfaces 7 a, 7 b, and 7 c thatdefine the reference portion 7, and are parallel to these surfaces 7 a,7 b, and 7 c. The auxiliary portion 8 helps define the position of theoptical element B1 by the reference portion 7.

At this time, when the reference and auxiliary portions 7 and 8 areformed to face each other, so that the position of the center of gravityof the optical element B1 is located within the region sandwichedbetween the reference and auxiliary portions 7 and 8, the opticalelement B1 can be held on the holding member with good balance when itis held by the holding member via the reference and auxiliary portions 7and 8.

The reference and auxiliary portions 7 and 8 are formed in considerationof an effective light ray transmission region inside the optical elementB1, and of course, they are formed on portions that do not shield thelight ray effective portion of the optical element B1.

In this embodiment, the reference portion 7 is defined by the surfaces 7a, 7 b, and 7 c which are parallel or perpendicular to the plane (Y′-Z′plane) including the reference axis 5. Alternatively, the referenceportion 7 may be defined with respect to a plane perpendicular to thereference axis 5 at an intersection A between the reference axis 5 andthe incident refracting surface R2 or an intersection B between thereference axis 5 and the exit refracting surface R8.

Furthermore, in this embodiment, the surfaces that form the referenceportion 7 are set to be parallel or perpendicular to the plane (Y′-Z′plane) including the reference axis 5 to help understand therelationship between the plane including the reference axis and thereference portion. Of course, the reference portion may be set to tilt apredetermined angle with respect to the plane (Y′-Z′ plane) includingthe reference axis of the optical element.

FIG. 3 is an explanatory showing a case wherein the optical element B1is held by holding members 9 and 11 using the reference portions 7 andthe auxiliary portion 8 of the first embodiment. In FIG. 3, referencenumeral 9 denotes a holding member which has a rectangular projection(coupling portion) 10 to be coupled to the reference portion 7 thereon.The holding member 9 is movably coupled to the main body (not shown) viaa moving surface. Also, reference numeral 11 denotes another holdingmember, which has a projection (coupling portion) 12 to be coupled tothe auxiliary portion 8 thereon.

A method of coupling the optical element B1 to the holding members willbe explained below. The surfaces 7 a, 7 b, and 7 c that define thereference portion 7 of the optical element B1 are joined to surfaces 10a, 10 b, and 10 c that define the projection 10 of the holding member 9to define the positions of the X′-, Y′-, and Z′-axes of the opticalelements B1 with respect to the holding member 9.

Subsequently, a surface 8 c that forms the auxiliary portion 8 of theoptical element B1 is joined to a surface 12 c that forms the projection12 of the holding member 11, and thereafter, the holding member 11 iscoupled to the holding member 9. In this manner, the optical element B1can be clamped by the two holding members and, hence, the opticalelement B1 is accurately and reliably held on the holding member 9 by auniform force with respect to the holding direction, i.e., theX′-direction.

Furthermore, since the surface 10 a of the projection 10 of the holdingmember 9 is formed to be parallel to the moving surface of the holdingmember 9, the plane (Y′-Z′ plane) including the reference axis 5, thesurface 7 a of the reference portion 7, and the moving surface of theholding member 9 become parallel to each other. With this arrangement,when the optical element B1 is moved together with the holding member 9upon focusing or zooming, a high degree of parallelism between themoving surface of the holding member 9 and the optical element B1 can beguaranteed, and the influences of, e.g., decentering of the referenceaxis that is likely to occur upon movement of the optical element B1,can be eliminated, thus preventing deterioration of the opticalperformance.

Also, in this embodiment, by modifying the holding method of the opticalelement B1 and the holding members, an optical system that produces lessharmful light rays can be built. This state will be explained below withreference to FIGS. 4 and 5.

FIG. 4 is a front view showing a case wherein the optical element B1 isimproperly coupled to the holding members 9 and 11 to build the opticalsystem. In this case, the reference portion 7 of the optical element B1is joined to the projection 10 of the holding member 9, the auxiliaryportion 8 is joined to the projection 12 of the holding member 11, andthe holding members 9 and 11 and the optical element B1 are held intight contact with each other.

At this time, harmful light rays 13 produced in the optical element B1are bound to pass through a side surface 14 of the optical element B1 toleave it. However, since the optical element B1 is in tight contact withthe holding member 9, the light rays 13 are immediately reflected by theholding member 9 and return to the optical element B1. As a consequence,the harmful light rays 13 may reach the image sensing surface.

FIG. 5 is a front view showing a case wherein the optical element of thefirst embodiment is coupled to the holding members 9 and 11 to form anoptical system. In FIG. 5, the holding members and the optical elementB1 are separated at a predetermined interval except for the jointportions between the reference portion 7 and the projection 10 of theholding member 9, and between the auxiliary portion 8 and the projection12 of the holding member 11. More specifically, the height (the heightin the X-direction in FIG. 5) of the projection 10 is determined to forma predetermined air gap between the optical element B1 and the holdingmember 9. When the optical element B1 is held to form an optical systemin this manner, the harmful light rays 13 produced inside the opticalelement B1 pass through the side surface 14 of the optical element 13and leave the optical element B1, thus preventing the light rays 13 frombeing reflected by the holding member 9 and re-entering the opticalelement B1.

[Second Embodiment]

FIG. 6 is a perspective view of an optical element according to thesecond embodiment of the present invention. In the first embodiment, theoptical element is held by one reference portion and one auxiliaryportion, while in the second embodiment, a plurality of auxiliaryportions are formed, and an optical element can be reliably held withhigher precision than in the first embodiment.

As shown in FIG. 6, an optical element B2 of the second embodiment has areference portion 7 and an auxiliary portion 8 on its two side surfacesas in the first embodiment, and also has four auxiliary portions 15, 16,17, and 18 at positions separated from the reference and auxiliaryportions 7 and 8 on the two side surfaces (forming surfaces).

More specifically, the auxiliary portions 17 and 18 are formed on theformation side of the reference portion 7 of the optical element B2, andthe auxiliary portions 15 and 16 are formed on the formation side of theauxiliary portion 8. Furthermore, as in the relationship between thereference and auxiliary portions 7 and 8, the auxiliary portions 15 and17, and the auxiliary portions 16 and 18 are formed to face each other.With this arrangement, even when the optical element B2 has a complexshape that cannot be held by a pair of reference and auxiliary portionswith good balance, the holding area for holding the optical element isincreased by the plurality of auxiliary portions, and the opticalelement B2 can be more securely held with high precision. The pluralityof auxiliary portions of the second embodiment strongly assist theposition determination of the optical element by the reference portion.

As for other arrangements, the same reference numerals denote the sameparts as in the first embodiment, and a detailed description thereofwill be omitted.

[Third Embodiment]

FIG. 7 is a perspective view of an optical element according to thethird embodiment of the present invention. In an optical element B3 ofthe third embodiment, the reference and auxiliary portions made up of aplurality of surfaces in the above embodiment are made up of round holesor elliptic holes, i.e., hole portions.

In FIG. 7, reference numeral 19 denotes a reference portion formed onthe optical element B3, which is a round hole (a hole portion) definedby a flat surface (bottom surface) 19 a parallel to the plane (Y′-Z′plane) including the reference axis and a cylindrical surface, a centralaxis 22 of which is perpendicular to the Y′-Z′ plane. Reference numeral20 denotes an auxiliary portion formed on the optical element B3, whichis an elliptic hole (a hole portion) defined by a flat surface 20 aparallel to the Y′-Z′ plane, and an elliptic cylindrical surface, thecentral axis of which is perpendicular to the Y′-Z′ plane and the majoraxis direction of which agrees with the Y′-direction.

Reference numeral 23 denotes a holding member which comprises aprojection (coupling portion) 24 to be coupled to the reference portion19, and a projection (coupling portion) 25 to be coupled to theauxiliary portion 20 thereon.

The round hole of the reference portion 19 defines the position of theoptical element B3 by defining the X′-axis by the central axis 22 anddefining the Y′-Z′ plane by the flat surface 19 a.

In a method of connecting the optical element B3 of the third embodimentto the holding member 23, the optical element B3 is held on the holdingmember 23 by fitting or adhering the projection 24 of the holding member23 and the reference portion 19, and the projection 25 of the holdingmember 23 and the auxiliary portion 20 to each other.

However, since rotation of the optical element B3 about the X′-axiscannot be restrained by fitting the reference portion 19 onto theprojection 24 of the holding member 23 alone, the auxiliary portion 20is defined by an elliptic hole in the third embodiment, so that theauxiliary portion 20 is fitted on the projection 25 of the holdingmember 23 to restrain movement in the Z′-direction, thus restrainingrotation of the optical element B3 about the X′-axis and coupling theholding member 23 and the optical element B3 more securely.

The reason why the auxiliary portion 20 is defined by an elliptic hole,the major axis direction of which agrees with the Y′-direction is asfollows. That is, even when the interval between the reference portion19 and the auxiliary portion 20 of the optical element B3 in theY′-direction varies, if the auxiliary portion 20 is defined by theabove-mentioned elliptic hole, the optical element B3 can be coupled tothe holding member 23 without being deformed while restraining rotationof the optical element B3 about the X′-axis, although the positionalrelationship between the projection 24 and the auxiliary portion 20 inthe Y′-direction shifts.

In the third embodiment, the reference and auxiliary portions are formedon only one side surface of the optical element B3. If the opticalelement B3 can be securely coupled to the holding member by only oneside, no auxiliary portion need be formed on the side surface opposingthe reference portion of the optical element B3.

As for other arrangements, the same reference numerals denote the sameparts as in the first embodiment, and a detailed description thereofwill be omitted.

[Fourth Embodiment]

FIG. 8 is a perspective view showing an optical element according to thefourth embodiment of the present invention, and an optical system usingthe same. An optical element B4 of the fourth embodiment is held byguide bars 31 and 32 fixed to a main body (not shown), and is movablefor attaining focusing or zooming using these guide bars 31 and 32 tobuild an optical system. Note that the guide bar 31 and the likeconstitute a guide means.

In the optical element B4 of the fourth embodiment, a hole portion 28serving as a reference portion is formed on a sleeve 27 formed on aportion of the element B4, and a guide portion 30 serving as anauxiliary portion is formed on a sleeve 35. A central axis 29 of thehole portion 28 is set to be parallel to the plane (Y′-Z′ plane)including the reference axis, and the hole portion 28 is movably fittedonto the guide bar 31, thereby defining the Z′-axis position of theoptical element B4.

Since rotation of the optical element B4 about the Z′-axis cannot berestrained by fitting of the hole portion 28 and the guide bar 31 alone,the guide portion 30 of the optical element B4 is movably fitted on theguide bar 32 parallel to the guide bar 31, thereby restraining rotationof the optical element B4 about the Z′-axis and also defining itsposition on the Y′-Z′ plane.

Note that the guide bars 31 and 32 are fixed to be parallel to the Y-Zplane of the absolute coordinate system of the optical system set on themain body, and the Y′-Z′ plane matches the Y-Z plane when the opticalelement B4 is attached to the two guide bars.

The sleeves 27 and 35 may be attached as independent members to theoptical element B4 after the optical element B4 is formed. However, inorder to obtain a high degree of parallelism between the central axis 29of the hole portion 28 and the Z′-axis, the sleeves 27 and 35, thereference portion 28, and the auxiliary portion 30 are preferablyintegrally formed on the optical element B4 in the manufacture of theoptical element B4.

With this arrangement, when the optical element B4 is moved for thepurpose of focusing or zooming, the parallelism between the guide bar 31and the optical element B4 can be maintained satisfactorily high.

Furthermore, in the fourth embodiment, since the central axis 29 of thehole portion 28 is set in the Y′-Z′ plane, changes in posture uponmovement of the optical element B4, especially, changes in posture uponrotation of the optical element B4 about the Y′- and Z′-axes, can befurther eliminated.

As for other arrangements, the same reference numerals denote the sameparts as in the first embodiment, and a detailed description thereofwill be omitted.

[Fifth Embodiment]

FIG. 9 is a perspective view of an optical element according to thefifth embodiment of the present invention. In an optical element B5 ofthe fifth embodiment, the reference and auxiliary portions of theoptical element B1 of the first embodiment are formed by shapesprojecting from the side surface (forming surface). In FIG. 9, referencenumeral 33 denotes a reference portion, which is a column defined by acylindrical surface with a central axis perpendicular to the Y′-Z′plane, and a surface parallel to the Y′-Z′ plane, and which projectsunlike the third embodiment. The reference portion 33 defines theposition of the optical element B5.

Reference numeral 34 denotes an auxiliary portion, which is defined by aflat surface 34 a parallel to the plane (Y′-Z′ plane) including thereference axis 5 of the optical element B5, a flat surface 34 b parallelto the X′-Y′ plane, a flat surface 34 c parallel to the Z′-X′ plane, andtwo more surfaces, and projects from the side surface (forming surface).

Reference numeral 36 denotes a holding member, on which a hole portion(coupling portion) 37 to be coupled to the reference portion 33, and ahole portion (coupling portion) 38 to be coupled to the auxiliaryportion 34 are formed.

In a method of connecting the optical element B5 of the fifth embodimentto the holding member 36, the optical element B5 is held on the holdingmember 36 by fitting or adhering the hole portion 37 of the holdingmember 36 onto the reference portion 33 contrary to the thirdembodiment.

However, since rotation of the optical element B5 about the X′-axiscannot be restrained by fitting of the hole portion and the projectionalone, in the fifth embodiment, the flat surface 34 b of the auxiliaryportion 34 is joined to a flat surface 38 b of the hole portion 38formed on the holding member 36, thereby restraining rotation of theoptical element B5 about the X′-axis.

Contrary to the above-mentioned embodiment, when the reference portionhas a rectangular shape projecting from the side surface (formingsurface), the position determination and rotation restrain of theoptical element B5 can be attained by only the reference portion withoutforming any auxiliary portion.

At this time, the reference portion is formed so that the position ofthe center of gravity of the optical element is located within a regionincluded in a projection of the reference portion in a directionperpendicular to the plane including the reference axis of the opticalelement. In this manner, the optical element can be held on the holdingmember with good balance.

As for other arrangements, the same reference numerals denote the sameparts as in the first embodiment, and a detailed description thereofwill be omitted.

[Sixth Embodiment]

FIG. 10 is a perspective view of an optical element according to thesixth embodiment of the present invention. In an optical element B6 ofthe sixth embodiment, the reference and auxiliary portions of theoptical element B1 of the first embodiment are formed as a combinationof a hole portion and a projection. More specifically, reference numeral40 denotes a reference portion formed as a projection; and 41, anauxiliary portion formed as a hole portion. In this manner, the shapesof the reference and auxiliary portions can be appropriately selected incorrespondence with situations.

As for other arrangements, the same reference numerals denote the sameparts as in the first embodiment, and a detailed description thereofwill be omitted.

The numerical value data of the optical system of this embodiment shownin FIG. 1 will be listed below.

[Numerical Value Data]

Horizontal half field angle=31.7

Vertical half field angle=24.8

Stop (aperture) Diameter=2.0

Image size=horizontal 4 mm×vertical 3 mm

i Yi Zi θi Di Ndi υdi 1 0.00 0.00 0.00 1.82 1 stop Optical Element B1 20.00 1.82 0.00 7.49 1.58310 30.20 refracting surface 3 0.00 9.30 18.499.86 1.58310 30.20 reflecting surface 4 −5.93 1.43 3.23 9.30 1.5831030.20 reflecting surface 5 −10.65 9.44 −12.55 8.90 1.58310 30.20reflecting surface 6 −11.50 0.58 −22.91 9.39 1.58310 30.20 reflectingsurface 7 −18.82 6.46 −25.63 8.02 1.58310 30.20 reflecting surface 8−18.82 −1.56 −0.01 3.68 1 refracting surface 9 −18.82 −5.24 −0.01 0.00 1image surface

Spherical Surface Shape

R1 surface R₁=∞

R2 surface R₂=−7.648

R8 surface R₈=10.757

R9 surface R₉=∞

Aspherical Surface Shape

R3 surface

a = −1.09716e + 01 b = −1.25390e + 01 t = 2.15145e + 01 C₀₂ = 0 C₂₀ = 0C₀₃ = 6.87152e − 05 C₂₁ = −1.21962e − 04 C₀₄ = 3.59209e − 05 C₂₂ =1.02173e − 04 C₄₀ = 4.95588e − 05

R4 surface

a = −2.34468e + 00 b = 4.88786e + 00 t = −3.56094e + 01 C₀₂ = 0 C₂₀ = 0C₀₃ = −4.48049e − 03 C₂₁ = −7.45433e − 03 C₀₄ = 1.81003e − 03 C₂₂ =2.09229e − 03 C₄₀ = −8.28024e − 04

R5 surface

a = −6.11985e + 00 b = 1.70396e + 01 t = −2.17033e + 01 C₀₂ = 0 C₂₀ = 0C₀₃ = −3.23467e − 04 C₂₁ = −1.07985e − 03 C₀₄ = −3.70249e − 05 C₂₂ =−1.74689e − 04 C₄₀ = −1.21908e − 04

R6 surface

a = ∞ b = ∞ t = 0 C₀₂ = 0 C₂₀ = 0 C₀₃ = 1.10097e − 03 C₂₁ = −3.73963e −04 C₀₄ = −1.59596e − 04 C₂₂ = −3.22152e − 04 C₄₀ = −1.74291e − 04

R7 surface

a = −2.11332e + 01 b = −1.31315e + 03 t = 1.70335e + 00 C₀₂ = 0 C₂₀ = 0C₀₃ = 8.29145e − 05 C₂₁ = −1.11374e − 03 C₀₄ = −2.50522e − 05 C₂₂ =−5.28330e − 05 C₄₀ = −2.91711e − 05

With the above-mentioned arrangement according to the present invention,a planar, low-profile optical element prepared by integrally forming arefracting surface for receiving a light beam, a plurality of reflectingsurfaces with curvatures, and a refracting surface for outputting thelight beam reflected by the plurality of reflecting surfaces on surfacesof a transparent member, is formed with a reference portion for definingthe position of the optical element in a specific direction with respectto a plane including an incident and exit reference axes of at least onereflecting surface of the optical element, or a reference portion fordefining the position of the optical element in a specific directionwith respect to a plane perpendicular to a reference axis at anintersection between the incident refracting surface or exit refractingsurface of the optical element, and the reference axis of the opticalelement. With this arrangement, an optical element which can define therelative positional relationship among the refracting surfaces and thedecentered reflecting surfaces with respect to the reference portions,can improve precision in the manufacture, assembly, and measurements ofthe optical element, and can prevent deterioration of opticalperformance, and an optical system using the optical element, can beachieved.

In addition, the present invention has the following effects.

The reference portion of the optical element is made easy to use bylimiting the specific direction to a parallel direction and/or aperpendicular direction with respect to the plane.

The optical element is accurately and securely held on the holdingmember or the like by forming an auxiliary portion for assisting theposition determination of the optical element in addition to thereference portion to be parallel or perpendicular to the referenceportion, and arranging at least one auxiliary portion to oppose thereference portion.

The holding member and the optical element are satisfactorily held uponholding the optical element by setting the reference and auxiliaryportions so that the position of the center of gravity of regionsandwiched between the reference and auxiliary portions substantiallymatches that of the optical element.

The reference portion and/or the auxiliary portion are/is formed on aregion other than the light ray effective portion of the opticalelement, so as to obtain an optical element which suffers less ghost,can prevent the reference portion and/or the auxiliary portion fromshielding effective light rays, and can reduce harmful light rays thatmay be produced by the reference portion and/or the auxiliary portion.

The reference portion and/or the auxiliary portion are/is formed by aplurality of flat surfaces, hole portions, or projections so as tosatisfactorily hold and fix the optical element in correspondence withevery situations.

A holding member that holds the optical element is designed to move orfix the optical element, and the holding member and the optical elementare precisely positioned by forming, on the holding member, portionsthat fit or join the reference portion and/or the auxiliary portionformed on the optical member.

When the optical element and the holding member for the optical elementare fitted or joined to each other, a predetermined air gap is formedbetween the holding member and the optical element in a region otherthan the fitting or joining portions, so as to obtain an optical elementwhich suffers less ghost, and can eliminate harmful light rays enteringthe optical element from the holding member as much as possible.

By integrally forming, on the optical element, a fitting hole forreceiving a guide bar for moving the optical element, a high degree ofparallelism between the central axis of the fitting hole and the planeincluding the reference axis can be assured.

By forming, on the optical element, a fitting hole for receiving theguide bar for moving the optical element, and setting the central axisof the fitting hole to be parallel to the incident reference axis of theoptical element, changes in posture upon movement of the optical elementcan be eliminated as much as possible when an optical system is builtusing the optical element.

By setting the central axis of the fitting hole to be parallel to theincident reference axis of the optical element in the plane includingthe reference axis of the optical element, changes in posture uponmovement of the optical element can be further eliminated when anoptical system is built using the optical element.

An embodiment in which the optical device of the present invention isapplied to an image sensing device will be explained below. Note thatthe present invention is not limited to an optical device having asolid-state image sensing device (e.g., a CCD) like in the embodiments,but may be similarly applied to, e.g., a silver halide camera and thelike.

[Seventh Embodiment]

FIG. 17 is a perspective view showing an image sensing device which usesfirst, second, and third optical elements according to the seventhembodiment of the present invention. FIG. 18 is a plan view of thedevice when viewed from a direction A in FIG. 17. FIG. 19 is a side viewof the device when viewed from a direction B in FIG. 17. FIG. 20 is aperspective view showing the state wherein the first, second, and thirdoptical elements are removed from the image sensing device shown in FIG.17, i.e., an explanatory view of various members other than the first,second, and third optical elements mounted on the image sensing device.FIG. 21 is an explanatory view of the reference optical axes of incidentlight and reflected light. FIG. 22 shows the optical paths of incidentlight and reflected light.

In FIGS. 17 to 22, reference numeral 201 denotes a first optical element(corresponding to the function of a front lens unit in a conventionallens) which consists of plastic, glass, or the like, and is formedintegrally with two refracting surfaces (an incident light surface 201 aand an exit light surface 201 f in FIG. 21), and four reflectingsurfaces (surfaces 201 b, 201 c, 201 d, and 201 e in FIG. 21). One endportion 201 h of the first optical element 201 is fixed to an attachmentportion 216 (see FIG. 20) of a base 209 by attachment screws 217. Thefirst optical element 201 is fixed to the base 209 at its one endportion 201 h to absorb expansion and shrinkage due to changes intemperature especially when the element 201 is plastic. As will bedescribed later, second and third optical elements 202 and 203 are fixedto the base at their one-end portions to be free to expand or shrink intheir longitudinal directions (nearly the directions of arrows C and D)according to the same idea as the first optical element 201. Since theone-end portions of the first, second, and third optical elements arefixed by screws, stresses produced by fastening the screws do notadversely influence portions (the optical path extending from theincident light surface 201 a to the reflecting surface 201 b) requiringoptical performance. Furthermore, when each optical element of thisembodiment is plastic, a gate (an injection port of a molten plasticmaterial upon injection molding) is formed on the side of an end face201 i of its one end portion 201 h so as not to adversely influence theportion that requires high optical performance.

Reference numeral 202 denotes a second optical element (corresponding toa variator in the conventional lens) which consists of plastic, glass,or the like, and is formed integrally with two refracting surfaces (anincident light surface 202 a and an exit light surface 202 g in FIG.21), and five reflecting surfaces (surfaces 202 b, 202 c, 202 d, 202 e,and 202 f in FIG. 21). Reference numeral 203 denotes a third opticalelement (corresponding to a compensator in the conventional lens) whichconsists of plastic, glass, or the like, and is formed integrally withtwo refracting surfaces (an incident light surface 203 a and an exitlight surface 203 g in FIG. 21), and four reflecting surfaces (surfaces203 b, 203 c, 203 d, 203 e, and 203 f in FIG. 21). Reference numeral 204denotes a stop mechanism (details are not shown). Reference numeral 205denotes a first movable base, which has a plurality of fitting holes 205a on its one end portion, and has a U-groove 205 b on the other endportion. These fitting holes 205 a are fitted on a first guide rail 215fixed to first guide rail fixing portions 211 of the base 209 by screws213 without any cluttering, and the U-groove 205 b is fitted on a secondguide rail 214 attached to second guide rail fixing portions 210 byscrews 213 so as to have a certain gap (in the directions of the arrowsC and D in FIG. 18). The first movable base 205 is smoothly slidably inthe direction of the arrow B and a direction opposite thereto along andwith reference to the guide rail 215 by a driving force of a steppingmotor 206 (to be described later). The first movable base 205 also hasan adhesion portion 205 d (see FIG. 20), to which the second opticalelement 202 is fixed by adhesion, on a portion roughly immediately abovethe fitting holes 205 a (in the direction point out of the page of FIG.18 or the direction of an arrow E in FIG. 19). The adhesion portion 205d can hold one end portion (exit light side) of the second opticalelement 202 by adhesion. As shown in FIG. 19, the second optical element202 and the first movable base 205 are in tight contact with each otheron the adhesion portion 205 d but a surface 205 e (see FIG. 20) otherthan the adhesion portion 205 d has a predetermined step with respect tothe adhesion portion 205 d. For this reason, a gap m is formed betweenthe optical element 202 and the surface 205 e, as shown in FIG. 19. Thisis to allow the optical element 202 to be free to expand or shrink inthe directions of the arrows C and D with reference to the adhesionportion 205 d when environmental changes (e.g., changes in temperatureR) have taken place, as described above. In this embodiment, the gap mis formed. Alternatively, the adhesion portion 205 d may be flush withthe surface 205 e without forming any gap m, and the optical element 202may be fixed by adhesion by only the adhesion portion 205 d. The firstmovable base 205 further has a rack portion 205 c (see FIGS. 18 and 20),which meshes with a screw shaft 207 of the first stepping motor 206.When the stepping motor 206 is driven by a driving control circuit (notshown), the first movable base 205 and the second optical element 202fixed thereto by adhesion are fed along the guide rail 215 by the rackportion 205 c and the screw shaft 207. Note that the first steppingmotor 206 is attached to a first angle 208, which is fixed to the base209.

In this embodiment, a stepping motor is used as the driving source.However, the present invention is not limited to this, and any otherdriving sources such as a DC motor, an ultrasonic wave motor, a voicecoil driving device, and the like may be used as long as they can drivethe first movable base 205 and the second optical element 202.

Reference numeral 218 denotes a second movable base, the structure ofwhich is substantially the same as that of the first movable base 205.The second movable base 218 has fitting holes 218 a on its one endportion, and a U-groove 218 b similar to the groove 205 b (see FIG. 20)on the other end portion. The fitting holes 218 a are fitted on thefirst guide rail 215 attached to the first guide rail fixing portions211 of the base 209 without any cluttering, and the U-groove 218 b isfitted on a third guide rail 222 attached to third guide rail fixingportions 212 of the base 209 by screws 213, so as to have a certain gapin the directions of the arrows C and D in FIG. 18. As in the firstmovable base 205, the second movable base 218 can smoothly move alongand with reference to the first guide rail 215.

The common guide rail 215 is used to serve as a reference since thefollowing merits and are expected as compared to using independent guiderails 215.

The second and third optical elements 202 and 203 move in the directionof the arrow B in FIG. 18 and a direction opposite thereto so as toattain zooming. In this case, a high-performance zoom mechanism requiresthat the exit optical axis from the second optical element 202 and theincident optical axis to the third optical element 203 (an optical axisof the reflecting surface 202 f to the reflecting surface 203 b shown inFIG. 21 to be described later) always agree with each other duringmovement of the optical elements 202 and 203 and at a stop positionafter movement. If independent guide rails 215 are used, the opticalaxes may not agree with each other due to assembly precision errors,parts variations, and the like, thus adversely influencing theperformance. If a common guide rail 215 is used, such problem can besolved.

A cost reduction can be attained by reducing the number of parts, thenumber of assembly steps, and the like.

The second movable base 218 has an adhesion portion 218 d for fixing thethird optical element 203 by adhesion on a portion roughly immediatelyabove the fitting holes 218 a, and the adhesion portion 218 d can holdone end portion (incident light side) of the third optical element 203by adhesion. Note that as in the first movable base 205, a predeterminedstep is formed between the adhesion portion 218 d and a surface 218 eother than the adhesion portion 218 d. This step also serves to absorbenvironmental changes (e.g., changes in temperature). Furthermore, thesecond movable base 218 has a rack portion 218 c (see FIGS. 18 and 20)as in the first movable base 205, which portion meshes with a screwshaft 220 of a second stepping motor 219. When the second stepping motor219 is driven by a driving control circuit (not shown), the secondmovable base 218 and the third optical element 203 adhered thereto arefed along the guide rail 215 by the second stepping motor 219 and thescrew shaft 220. Note that the second stepping motor 219 is attached toa second angle 221, which is fixed to the base 209.

Reference numeral 223 denotes an optical low-pass filter; 224, an IR(infrared ray) blocking filter; and 225, a CCD (solid-state imagesensing device), which are known means required for converting opticalinformation into an electrical signal, and are used for convertingoptical information which has passed through the first, second, andthird optical elements 201, 202, and 203 into an electrical signal, asshown in FIG. 21. Note that the optical low-pass filter 223, IR blockingfilter 224, and CCD 225 normally have a predetermined structure, and areintegrally coupled and attached. However, this structure is not shown.Also, the CCD 225 is normally connected to a signal processing circuit,but this portion is not shown, either. Reference numeral 226 denotes aCCD attachment plate to which the CCD 225 is attached; 227, an angle forattaching these members to the base 209; and 232, a projection (see FIG.18; it seems recessed in the direction of the arrow B in FIG. 17) formedby drawing the angle 227 in the direction of the arrow B in FIG. 17. TheCCD attachment plate 226 is coupled to the angle 227 to abut against theprojection 232 by screws 230 and a screw 228 via a spring washer 229.This structure is used to adjust the tilt angle of the CCD 225 so thatlight can enter the CCD 225 at a predetermined incident angle, whenlight leaving the exit surface 203 g of the third optical element 203cannot enter the CCD 225 in a direction perpendicular to the surface ofthe CCD 225 due to parts precision errors, assembly errors, and thelike. That is, the screws 228 and 230 are appropriately fastened orloosened to determine the position of the CCD 225 about the projection232 as a fulcrum.

The reason why the second optical element 202 is fixed by adhesion to aposition roughly immediately above the fitting hole 205 a of the firstmovable base 205 (roughly immediately below the exit optical axis fromthe second optical element 202; each optical axis extends along oneplane in FIG. 21, and a first guide rail 215 is present in or in thevicinity of a plane which crosses that plane at a position of theoptical axis of the reflecting surface 202 f to the reflecting surface203 b, and is perpendicular to that plane, and is nearly parallel to theoptical axis of the reflecting surface 202 f to the reflecting surface203 b), and the third optical element 203 is fixed by adhesion to aposition roughly immediately above the fitting hole of the secondmovable base 218 (roughly immediately below the incident optical axis ofthe third optical element 203) will be explained below.

As described above, both the movable bases 205 and 218 that respectivelyhold the second and third optical elements 202 and 203 are fitted on thefirst guide rail 215, and are movable along it.

When ambient temperature changes, the optical element 202 expands orshrinks. Since the exit optical axis (light rays leaving the reflectedsurface 202 f in FIG. 21) side of the optical element 202 is adhered tothe adhesion portion 205 d of the first movable base 205 roughlyimmediately above the fitting holes 205 a, it expands in the directionof the arrow C or shrinks in the direction of the arrow D in FIG. 18with reference to that adhered portion. On the other hand, since theincident optical axis (light rays entering the surface 203 a in FIG. 21)of the third optical element 203 is adhered to the adhesion portion 218d of the first movable base 205 roughly immediately above the fittingholes 218 a, it expands in the direction of the arrow D or shrinks inthe direction of the arrow C in FIG. 18 with reference to that adheredportion. That is, the two optical elements can expand or shrink inopposite directions with reference to the first guide rail 215. Sincethe exit optical axis from the second optical element 202 and theincident optical axis to the third optical element (the optical axisextending from the surface 202 f to the surface 203 b in FIG. 21) ispresent roughly immediately above the guide rail 215, these two opticalelements 202 and 203 expand or shrink in opposite directions withreference to the exit optical axis from the second optical element 202and the incident optical axis to the third optical element 203. As aconsequence, light leaving the second optical element 202 can always belaunched on an identical position of the incident light surface 203 a(see FIG. 21) without being influenced by changes in temperature.

On the other hand, since the first optical element 201 is fixed to theattachment portion 216 from the base 209 at its one end portion 201 hclose to the first guide rail 215, it expands in nearly the direction ofthe arrow C or shrinks in the direction of the arrow D with reference toits one end portion 201 h. Such expansion and shrinkage take place inthe same directions as those of the second optical element 202. Also, inthe first optical element, the length in the direction of the arrow Cfrom the position of the attachment screw 217 to the exit light surface201 f is about 40 mm, while in the second optical element 202, the sizein the direction of the arrow C from the adhered portion (the positionof the exit optical axis from the surface 202 f) to the incident lightsurface 202 a is about 45 mm, i.e., the difference between these sizesis small. Hence, the two optical elements have substantially equalexpansion/shrinkage amounts due to changes in temperature. With thisstructure, light leaving the exit light surface 201 f strikes asubstantially identical position on the incident light surface 202 a ofthe second optical element 202 without being influenced by changes intemperature. That is, the above-mentioned structure can prevent opticalperformance from deteriorating due to changes in temperature.

Note that the position of light leaving the third optical element 203(i.e., light rays coming from the surface 203 f) shifts in the directionof the arrow C or D in FIG. 18 due to changes in temperature. However,no serious problem is posed since these light rays enter the CCD 225which does not particularly require high attachment precision in thedirections of the arrows C and D with respect to the third opticalelement 203 (the precision can be low).

The layout of the stepping motors 206 and 219 will be explained below.

In FIG. 18, the first stepping motor 206 is arranged at a positionsurrounded by the first, second, and third optical elements 201, 202,and 203. On the other hand, the second stepping motor 219 is arranged ata position surrounded by the second and third optical elements 202 and203, and the CCD 225. These places correspond to dead spaces in thelayout of the optical elements, and when stepping motors are installedat these places, the overall space factor can be improved, thuscontributing to a size reduction of the device. Furthermore, thesepositions correspond to the vicinities of the first guide rail 215serving as a reference upon movement of the first and second movablebases 205 and 218, and can minimize twisting or the like produced uponmovement of the individual movable bases. Hence, the optical elementscan be moved with high precision.

Since the first guide rail 215 serving as a reference is arranged in thevicinity of light that leaves the second optical element 202 and lightthat enters the third optical element 203 (an identical optical axis,i.e., the optical axis of the surface 202 f to the surface 203 b), theadverse influences of cluttering or the like upon zoom movement on theoptical axis of the surface 202 f to the surface 203 b can be minimized.Note that a common guide rail may be arranged in the vicinity of theoptical axis of the surface 201 e to the surface 202 b in FIG. 21, butis preferably arranged in the vicinity of the optical axis of thesurface 202 f to the surface 203 b for the following reason .

That is, the first optical element 201 is fixed in position; it does notmove. On the contrary, the second and third optical elements 202 and 203always move upon zooming. More specifically, when the guide rail 215serving as a reference is arranged in the vicinity of the optical axisof the surface 202 f to the surface 203 b that suffers many variationfactors due to cluttering and the like, the variation factors can besuppressed, and a zoom mechanism with higher precision can be realized.

The operation for fetching an image by the CCD 225 in theabove-mentioned arrangement will be described below with reference toFIG. 21. Note that FIG. 21 illustrates only the optical path of chieflight rays, the behavior of the entire light beam is disclosed in, e.g.,Japanese Patent Application Nos. 7-65109 and 7-123256, and a detaileddescription thereof will be omitted.

In FIG. 21, image information of an object 231 is incident on theincident light surface 201 a of the first optical element 201. Since thefirst optical element 201 consists of plastic, glass, or the like, asdescribed above, the image information is refracted by the refractingpower of the incident light surface 201 a upon incidence. In this case,a driving control circuit (not shown) drives the stop mechanism 204 onthe basis of brightness information from a light amount detectionmechanism (not shown) to adjust the incident light amount to be apredetermined value. The light entering the incident light surface 201 ais reflected in turn by the reflecting surfaces 201 b, 201 c, 201 d, and201 e, and leaves the first optical element 201 after it is similarlyrefracted by the refracting power of the exit light surface 201 f. Thelight then becomes incident on the incident light surface 202 a of thesecond optical element 202. In this case, the light is refracted by therefracting power of the surface 202 a. The light is reflected in turn bythe reflecting surfaces 202 b, 202 c, 202 d, 202 e, and 202 f of thesecond optical element 202, and leaves the second optical element 202after it is refracted by the refracting power of the exit light surface202 g. This light enters the third optical element 203 after it becomesrefracted light by the incident light surface 203 a of the third opticalelement 203, is reflected in turn by the surfaces 203 b, 203 c, 203 d,203 e, and 203 f, and leaves the third optical element 203 from the exitlight surface 203 g as refracted light. The light from the exit lightsurface 203 g passes through the low-pass filter 223 and the IR blockingfilter 224, and forms an image on the CCD 225. The image informationfrom the CCD 225 is processed by a signal processing circuit or the like(not shown), and is finally displayed on a display device (not shown).The operator who observes the displayed image operates an operationdevice (not shown) to adjust the object image to a desired field angle.This operation corresponds to that of a zoom switch toward the telephotoor wide-angle side in a conventional video camera or electronic stillcamera. In general, auto-focusing is done after zooming, but its controlmethod is a state-of-the-art technique. Furthermore, during thisinterval, a control unit (not shown) controls the stop mechanism 204 toobtain desired lightness.

The control of the second and third optical elements 202 and 203 uponoperation of the zoom switch by the operator will be explained below.

When the operator operates the zoom switch toward the telephoto side,the stepping motors 206 and 219 (see FIG. 18) rotate in a predetermineddirection in accordance with a control signal from a control unit (notshown). At the same time, the screw shafts 207 and 220 are rotated.Since the screw shafts 207 and 220 respectively mesh (threadably fit)with the rack portion 205 c of the first movable base 205 and the rackportion 218 c of the second movable base 218, the second and thirdoptical elements 202 and 203 move by a predetermined amount in thedirection of the arrow B in FIGS. 17, 18, and 21. When the operatorstops the operation at an appropriate position, the first or secondmovable base 205 or 218 is controlled to move by a very small amount inthe direction of the arrow B or a direction opposite thereto, thusbringing a focal point on the CCD 225. Note that the state illustratedin FIGS. 18 and 21 is close to the wide-angle side. When the zoom switchis operated from this state toward the wide-angle side, the second andthird optical elements 202 and 203 move in the direction opposite to thedirection of the arrow B, but their moving amount is smaller than thatwhen they move toward the telephoto side. FIG. 22 is an optical pathdiagram of light rays by the optical elements of this embodiment, andillustrates, as an example, the propagation state of light rays whileforming images inside the optical elements. Note that the behavior of alight beam upon movement of a plurality of optical elements each havinga plurality of refracting surfaces and a plurality of reflectingsurfaces by the telephoto/wide-angle operation is described in, e.g.,Japanese Patent Application Nos. 7-65109 and 7-123256, and a detaileddescription thereof will be omitted.

Note that the stop mechanism 204 is subjected to predetermined controlby a predetermined control signal during such zoom operations, needlessto say. Furthermore, when the image sensing device is an electronicstill camera, since a shutter is required, the stop mechanism 204 may beprovided with a shutter function, a CCD with a shutter function may bemounted, or a shutter may be added.

As described above, according to this embodiment, in an optical devicehaving an optical element in which a light beam is incident from onerefracting surface, is reflected by a plurality of reflecting surfaces,and departs from the element from another refracting surface, theoptical performance can be prevented from deteriorating due to stressupon fixing the optical element and changes in temperature.

Also, according to this embodiment, in an optical device which comprisesa zoom optical system having a plurality of optical elements in each ofwhich a light beam is incident from one refracting surface, is reflectedby a plurality of reflecting surfaces, and leaves the element fromanother refracting surface, and a driving means for driving the zoomoptical system to attain zooming, the following effects i to iv can beobtained.

i. The individual optical elements are fixed to the correspondingmovable bases on the side of an optical axis where light leaving oneoptical element enters the other optical element, and a common referenceguide rail is used for the movable bases and is arranged in the vicinityof the optical axis.

As a result, the adverse influences of expansion/shrinkage of theoptical elements arising from changes in temperature and resultingchanges in refracting power on image quality can be removed.

ii. Since the individual optical elements are fixed to the correspondingmovable bases at their one-end side and at the side of the optical axis,adverse influences on image quality can be similarly removed.

iii. When the thermal expansion coefficient of the optical elementsassumes a value close to that of the movable bases to which the opticalelements are attached, the attachment position of one optical element tothe first movable base, and that of the other optical element to thesecond movable base are determined to be symmetrical about the commonreference guide, thereby similarly removing adverse influences on imagequality.

iv. The fixing position of the stationary first optical element to thebase, and the fixing positions of the movable second and third opticalelements to the first and second movable bases are set on the referenceguide rail side, thereby similarly removing adverse influences on imagequality.

According to this embodiment, dead spaces can be effectively used toachieve a size reduction of an image sensing device that comprises azoom optical system in which a light beam is incident from onerefracting surface, is reflected by a plurality of reflecting surfaces,and leaves the element from another refracting surface, and a drivingmeans for driving the zoom optical system to attain zooming.

Furthermore, according to this embodiment, the following effects v andvi can be obtained.

v. In the arrangement that attains zooming by moving two opticalelements in an identical optical axis direction in which the exitoptical axis from one element integrally formed with a plurality ofrefracting surfaces and a plurality of reflecting surfaces becomes theincident optical axis of the other similar optical element, a commonguide rail for moving these elements is arranged in the vicinity of theidentical optical axis, thus enabling high-precision zoom driving.

vi. Since the optical elements are driven in the vicinity of a guiderail, twisting or the like can be suppressed from being produced, andhigh-precision feeding can be realized.

[Eighth Embodiment]

FIG. 23 is a plan view of an image sensing device according to theeighth embodiment of the present invention. FIG. 24 is a side view ofFIG. 23. FIGS. 23 and 24 respectively correspond to FIGS. 18 and 19 ofthe seventh embodiment. In the seventh embodiment, the second and thirdoptical elements 202 and 203 are moved using the stepping motors 206 and219 and the screw shafts 207 and 220. However, in this embodiment, a camfeed mechanism is adopted, and the layout of the stepping motors ischanged. Such modifications are made to improve the space factor ascompared to the seventh embodiment and, more specifically, to decreasethe thickness of the mechanical structure. Furthermore, the attachmentmethods of the second and third optical elements 202 and 203 arechanged. Note that the same reference numerals in FIGS. 23 and 24 denotethe same parts as in the seventh embodiment, and a detailed descriptionthereof will be omitted.

Reference numeral 301 denotes a first optical element (corresponding toreference numeral 201 in FIG. 17); and 302, a second optical element(corresponding to reference numeral 202 in FIG. 17). The difference fromthe seventh embodiment is that an attachment portion 302 h is formed onone end portion of the second optical element 302. As described above,this structure is exploited to prevent stress produced upon fasteningthe screws from adversely influencing the optical performance. In thisembodiment, the shape is improved, and the attachment portion 302 h isformed on the second optical element 302 to sandwich slits 302 itherebetween (see FIG. 24). This attachment portion 302 h is fixed to anupright portion 305 f of a first movable base 305 (corresponding toreference numeral 205 in FIG. 17) by screws 350.

As another attachment shape that does not adversely influence theportion requiring high optical performance, an example shown in FIG. 25is also available. In FIG. 25, reference numeral 402 denotes a secondoptical element according to the ninth embodiment. Reference numeral 402h denotes an attachment portion formed on one end portion of the secondoptical element 402 like the attachment portion 302 h. In thisembodiment, however, groove portions 402 i are formed as fasteningstress relief portions in place of the slits 302 i. Note that the shapeshown in FIG. 25 allows mold release in the directions of arrows F andG. That is, the shape of this embodiment takes the mold structure intoconsideration. The first, second, and third optical elements 201, 202,and 203 also take the mold structure into consideration. In thisembodiment, the attachment portion is formed by protruding one endportion of the optical element in its longitudinal direction. In orderto prevent fastening stress from adversely influencing the opticalperformance, the attachment portion may protrude from a positionseparate from the refracting or reflecting surface of the opticalelement and perpendicular to these surfaces, more particularly, in adirection pointing out of or into the page, and may be attached to afixing member, thus obtaining the same effect as in the aboveembodiments.

Referring back to FIG. 23, reference numeral 303 denotes a third opticalelement (corresponding to reference numeral 203 in FIG. 17), which isformed with an attachment portion 303 h and slits 303 i (not shown) asin the second optical element 302. The third optical element 303 isfixed to an upright portion 318 f of a second movable base 318 by screws351. Note that the attachment portions of the second and third opticalelements 302 and 303 are formed on the side of a first guide rail 215serving as a reference. This structure is used in consideration ofexpansion and shrinkage with temperature as in the seventh embodiment.

Furthermore, in this embodiment, the fixing position of the secondoptical element 302 to the first movable base 305 by the screws isnearly symmetrical to that of the third optical element 303 to thesecond movable base 318 by the screws to sandwich the first guide rail215 therebetween in FIG. 23 (the distances from the guide rail 215 tothese elements are also nearly equal to each other). When both theoptical elements and movable bases consist of materials having nearlyequal thermal expansion coefficients, e.g., when they consist of plasticmaterials, such layout can also prevent expansion/shrinkage due tochanges in temperature from adversely influencing the opticalperformance. The advantage of such layout will be explained in detailbelow taking the second optical element 302 as an example.

For example, when the temperature rises, an attachment portion 305 f ofthe first movable base 305 shifts in the direction of an arrow D due toexpansion with reference to the first guide rail 215. However, thesecond optical element 302 shifts in the direction of an arrow C(opposite to the direction of the arrow D) by expansion with referenceto its attachment portion 302 h. That is, since these elements expand indirections to cancel each other, an optical axis of a surface 202 f to asurface 203 b (exit light from the second optical element 302, incidentlight to the third optical element 303) maintains a position roughlyimmediately above the first guide rail 215. Even when these elementsshrink after the temperature drops, they shrink in directions to canceleach other, and the optical axis of the surface 202 f→the surface 203 bcan keep its position roughly immediately above the first guide rail215. The same applies to the relationship between the third opticalelement 303 and the second movable base 318. With this arrangement, theexit optical axis from the second optical element 303 always guides anincident light beam onto a predetermined position of the third opticalelement 303, and the optical performance never deteriorates.

Projections (bulges pointing into the page in FIG. 23) 302 g and 303 gare formed on both the second and third optical elements 302 and 303 inFIG. 23.

These projections are formed for the following reason.

In the seventh embodiment, the optical element is fixed to the movablebase by an adhesive. In the manufacture, it is assumed that the opticalelement is three-dimensionally positioned using a jig, and is fixed byan adhesive. In this embodiment, for example, as for the second opticalelement 302 (the same applies to the third optical element 303), theprojections 302 g are formed with high precision, and are used as areference upon attachment. With this arrangement, after the opticalelement is placed on the movable base, it can be fixed to the movablebase by only fastening the screws 350.

Note that a total of three projections must be formed at positionsseparated by largest possible distances in the longitudinal direction(the directions of the arrows C and D) and at a position separated by alargest possible distance in the widthwise direction (a directionperpendicular to the directions of the arrows C and D), so that theoptical element can be stably placed on the first movable base 305.Also, butt surfaces may be formed on the first movable base 305 asneeded with high precision to attain high-precision positioning.

If the optical element consists of glass, the second optical element302, for example, may have no attachment portion 302 h (the same shapeas that of the second optical element 202 of the seventh embodiment),and at least one of the projections 302 g may be fixed by an adhesive.In this case, since the positioning portion is fixed by an adhesive, theoptical element can be positioned and fixed with high precision.

Reference numeral 306 denotes a first driving motor for moving the firstmovable base 305 along the first guide rail 215. The first driving motor306 has a tongue-like cam portion 306 c with an elongated hole portion306 a, which cam portion is coupled to a shaft portion 320 (see FIG.24). Note that the elongated hole portion 306 a engages with an engagingpin 305 g formed on the first movable base 305. In FIG. 23, when thefirst driving motor 306 rotates from a chain line P to a chain line Q,the first movable base 305 and the second optical element 302 fixedthereto move in the direction of the arrow B. Note that FIG. 23illustrates the positions of the cam portion 306 c by two-dashed chainlines when the driving motor 306 has rotated a predetermined angle.

The second movable base 318 and the third optical element 303 fixedthereto move by a second driving motor 319 in the direction of the arrowB or in a direction opposite thereto. As in the first driving motor 306,the second driving motor 319 has a tongue-like cam portion 319 c with anelongated hole portion 319 a, which cam portion is coupled to a shaftportion (not shown), and the elongated hole portion 319 a engages withan engaging pin 318 g formed on the second movable base 318. With thisstructure, the second movable base 318 and the third optical element 303can move in the direction of the arrow B or in a direction oppositethereto. Note that the positions of the cam portion 319 c upon rotationof the second driving motor 319 by a predetermined angle are indicatedby two-dashed chain lines.

The layout of the driving motors 306 and 319 in this embodiment will bedescribed below.

In FIG. 23, the first driving motor 306 is arranged among the second andthird optical elements 302 and 303, and a CCD 225, and the seconddriving motor 319 is arranged among the first, second, and third opticalelements 301, 302, and 303. This layout is the same as that in theseventh embodiment to attain space savings and a size reduction of thedevice. However, in the seventh embodiment, the stepping motors 206 and219 are merely arranged on dead spaces in the plan view (see FIG. 18).By contrast, in this embodiment, the driving motors 306 and 319 arearranged so that their motor shaft directions are perpendicular to thepage of FIG. 23 (in the seventh embodiment, the shaft directions areparallel to the page). Furthermore, the moving mechanism adopts a cammechanism. For this reason, as compared to the seventh embodiment, thedriving motors 306 and 319 can shift in the direction of the arrow E inFIG. 24. As a result, the spaces where the stepping motors 206 and 219in the seventh embodiment are arranged can be used as those forarranging a printed circuit board, and the like, and the space factor ofthe whole device can be improved, thus more contributing to a sizereduction. In this embodiment, the cam mechanism is adopted.Alternatively, a gear train such as a spur gear, helical gear, and thelike may be used to realize a low-profile structure, thus obtaining thesame effect as in the above embodiment.

As described above, according to this embodiment, the same effect as inthe seventh embodiment can be obtained.

Also, according to this embodiment, the same effect as in the seventhembodiment can be obtained, and since slits or grooves are formed on theprojection of each optical element, the influence on the opticalperformance due to fixing stress can be further reduced.

Furthermore, according to this embodiment, a compact, low-profile imagesensing device can be realized as in the seventh embodiment.

As described above, according to the present invention, deterioration ofthe optical performance of the optical element owing to the way offixing the optical element can be prevented.

According to the present invention, in an optical device which comprisesa zoom optical system having a plurality of optical elements in each ofwhich a light beam is incident from one refracting surface, is reflectedby a plurality of reflecting surfaces, and leaves the element fromanother refracting surface, and a driving means for driving the zoomoptical system to attain zooming, deterioration of images caused byexpansion/shrinkage of the optical elements due to changes intemperature, and changes in refracting power due to theexpansion/shrinkage can be prevented.

Also, according to the present invention, a size reduction of an opticaldevice that comprises a zoom optical system in which a light beam isincident from one refracting surface, is reflected by a plurality ofreflecting surfaces, and leaves the element from another refractingsurface, and a driving means for driving the zoom optical system toattain zooming can be attained.

Furthermore, according to the present invention, in an optical devicewhich comprises a zoom optical system having a plurality of opticalelements in each of which a light beam is incident from one refractingsurface, is reflected by a plurality of reflecting surfaces, and leavesthe element from another refracting surface, and a driving means fordriving the zoom optical system to attain zooming, the zoom driving canbe done with high precision.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:
 1. An optical element prepared by integrallyforming, on surfaces of a transparent member, a refracting surface forreceiving a light beam, a plurality of reflecting surfaces formedcurvatures having optical powers, and a refracting surface foroutputting the light beam reflected by the plurality of reflectingsurfaces, comprising: a reference portion for defining a position ofsaid optical element in a predetermined direction with respect to aplane including an incident and exit reference axes of at least onereflecting surface of said optical element.
 2. The element according toclaim 1, wherein the predetermined direction is a direction parallel orperpendicular to the plane including the reference axes.
 3. The elementaccording to claim 2, wherein said reference portion has a flat surfaceparallel to the plane including the reference axis of said opticalelement and at least two flat surfaces perpendicular to the plane. 4.The element according to claim 1, wherein a center of gravity of saidoptical element is present within a region included in a projection ofsaid reference portion onto said optical element in a directionperpendicular to the plane including the reference axis of said opticalelement.
 5. The element according to claim 1, wherein said referenceportion is formed on a region other than a light ray effective portionof said optical element.
 6. The element according to claim 1, whereinsaid reference portion is made up of a plurality of flat surfaces. 7.The element according to claim 1, wherein said reference portion is ahole portion or projected portion formed on said optical element.
 8. Theelement according to claim 7, wherein the hole portion or the projectedportion has a cylindrical surface having a central axis perpendicular tothe plane including the reference axis of said optical element.
 9. Theelement according to claim 1, wherein an auxiliary portion for assistingin determining the position of said optical element is formed on saidoptical element.
 10. The element according to claim 9, Wherein saidauxiliary portion is set to be parallel or perpendicular to saidreference portion.
 11. The element according to claim 10, wherein aplurality of auxiliary portions equivalent to said auxiliary portionsare formed, and at least one of the auxiliary portions faces saidreference portion.
 12. The element according to claim 11, wherein acenter of gravity of said optical element is present in a regionsandwiched between said reference portion and the auxiliary portionfacing said reference portion.
 13. The element according to claim 9,wherein said reference portion and said auxiliary portion are formed ona region other than a light ray effective portion of said opticalelement.
 14. The element according to claim 13, wherein said auxiliaryportion is made up of a plurality of flat surfaces.
 15. The elementaccording to claim 14, wherein said auxiliary portion has a flat surfaceparallel to the plane including the reference axis of said opticalelement and at least one flat surface perpendicular to the plane. 16.The element according to claim 13, wherein said auxiliary portion is ahole portion formed on said optical element.
 17. The element accordingto claim 16, wherein the hole portion or the projected portion has acylindrical surface having a central axis perpendicular to the planeincluding the reference axis of said optical element.
 18. The elementaccording to claim 16, wherein the hole portion or the projected portionhas an elliptic cylindrical surface having a central axis perpendicularto the plane including the reference axis of said optical element. 19.An optical system formed by stationarily or movably holding said opticalelement of claim 9 via a holding member, which has a coupling portionfitted or coupled to said reference portion.
 20. The system according toclaim 19, wherein a predetermined air layer is formed between saidholding member and said optical element except for said coupling portionof said holding member.
 21. An optical system formed by stationarily ormovably holding said optical element of claim 1 via a holding member,which has a coupling portion fitted or coupled to said referenceportion.
 22. The system according to claim 21 wherein a predeterminedair layer is formed between said holding member and said optical elementexcept for said coupling portion of said holding member.
 23. An opticalelement prepared by integrally forming, on surfaces of a transparentmember, a refracting surface for receiving a light beam, a plurality ofreflecting surfaces formed curvatures having optical powers, and arefracting surface for outputting the light beam reflected by theplurality of reflecting surfaces, comprising: a reference portion fordefining a position of said optical element in a predetermined directionwith respect to a plane perpendicular to a reference axis of saidoptical element at an intersection between the incident refractingsurface or exit refracting surface and the reference axis of saidoptical element.
 24. The element according to claim 23, wherein thepredetermined direction is a direction parallel or perpendicular to theplane perpendicular to the reference axis.
 25. The element according toclaim 24, wherein said reference portion has a flat surface parallel tothe plane including the reference axis of said optical element and atleast two flat surfaces perpendicular to the plane.
 26. The elementaccording to claim 23, wherein a center of gravity of said opticalelement is present within a region included in a projection of saidreference portion onto said optical element in a direction perpendicularto the plane including the reference axis of said optical element. 27.The element according to claim 23, wherein said reference portion isformed on a region other than a light ray effective portion of saidoptical element.
 28. The element according to claim 23, wherein saidreference portion is made up of a plurality of flat surfaces.
 29. Theelement according to claim 23, wherein said reference portion is a holeportion or projected portion formed on said optical element.
 30. Theelement according to claim 29, wherein the hole portion or the projectedportion has a cylindrical surface having a central axis perpendicular tothe plane including the reference axis of said optical element.
 31. Theelement according to claim 23, wherein an auxiliary portion forassisting in determining the position of said optical element is formedon said optical element.
 32. The element according to claim 31, whereinsaid auxiliary portion is set to be parallel or perpendicular to saidreference portion.
 33. The element according to claim 32, wherein aplurality of auxiliary portions equivalent to said auxiliary portionsare formed, and at least one of the auxiliary portions faces saidreference portion.
 34. The element according to claim 33, wherein acenter of gravity of said optical element is present in a regionsandwiched between said reference portion and the auxiliary portionfacing said reference portion.
 35. The element according to claim 31,wherein said reference portion and said auxiliary portion are formed ona region other than a light ray effective portion of said opticalelement.
 36. The element according to claim 35, wherein said auxiliaryportion is made up of a plurality of flat surfaces.
 37. The elementaccording to claim 36, wherein said auxiliary portion has a flat surfaceparallel to the plane including the reference axis of said opticalelement and at least one flat surface perpendicular to the plane. 38.The element according to claim 35, wherein said auxiliary portion is ahole portion formed on said optical element.
 39. The element accordingto claim 38, wherein the hole portion or the projected portion has acylindrical surface having a central axis perpendicular to the planeincluding the reference axis of said optical element.
 40. The elementaccording to claim 38, wherein the hole portion or the projected portionhas an elliptic cylindrical surface having a central axis perpendicularto the plane including the reference axis of said optical element. 41.An optical system formed by stationarily or movably holding said opticalelement of claim 31 via a holding member, which has a coupling portionfitted or coupled to said reference portion.
 42. The system according toclaim 41, wherein a predetermined air layer is formed between saidholding member and said optical element except for said coupling portionof said holding member.
 43. An optical system formed by stationarily ormovably holding said optical element of claim 23 via a holding member,which has a coupling portion fitted or coupled to said referenceportion.
 44. The system according to claim 43, wherein a predeterminedair layer is formed between said holding member and said optical elementexcept for said coupling portion of said holding member.